The present invention relates to a method and a supply system for supplying pellets of hot melt ink to a printer comprising an ink reservoir having an inlet port through which the ink pellets are supplied, and a closure member for sealingly closing the inlet port.
Ink jet printers operating with hot melt ink, i.e. with ink that is solid at room temperature, comprise an ink reservoir which can be heated in order to melt the ink and to keep it in the liquid state so that it can be supplied to the printhead. The ink can be supplied to this ink reservoir in the form of pellets which are then melted in the ink reservoir.
If the inlet port of the ink reservoir is left open while the printer is operating, a vapor of melted and evaporated ink could escape from the ink reservoir, whereby the other components of the printer would become soiled with condensated ink. It is therefore desirable to provide a closure member for sealingly closing the inlet port. This, however, has the consequence that the process of introducing ink pellets into the ink reservoir becomes more complicated and the more difficult to automate, because it is necessary to remove and to re-install the closure member each time an ink pellet is added to the ink reservoir.
EP-A-0 340 533 discloses a refill cartridge for hot melt ink in which a pellet of solidified ink is contained in a hood-shaped envelope which can be placed onto the inlet port of the ink reservoir with the open side facing downward. Then, by deforming the walls of the envelope, the ink pellet can be pressed out so that it can be dropped into the ink reservoir.
U.S. Pat. No. 4 864 330 discloses a refill cartridge in which a pellet of hot melt ink is connected to a handle. In this case, the pellet is held with the handle and placed into the inlet port of the ink reservoir. Since the pellet is held non-rotatably in this inlet port by a key structure, the handle can be broken away by turning the same, so that the pellet alone drops into the ink reservoir.
Although the ink pellets disclosed in these documents are temporarily held in the inlet port of the ink reservoir, there still remains the necessity to provide a closure member for sealing the inlet port during the time periods in which the printer is operating and no new pellet is added.
It is an object of the present invention to provide a method and a supply system for supplying pellets of hot melt ink to the printer in which the process of opening the inlet port of the ink reservoir, passing the ink pellet therethrough and re-sealing the inlet port is facilitated.
According to the present invention, this object is achieved by a method in which one of the ink pellets is fitted in the inlet port so as to serve as said closure member, and, when this pellet is to be supplied to the ink reservoir, it is pressed through the inlet port and a new pellet replaces it as a new closure member.
Correspondingly, the ink supply system according to the present invention is characterized in that the closure member consists of an ink pellet held in the inlet port by friction, but eventually pushed through into the ink reservoir to be replaced by a new closure member.
Thus, when a new ink pellet is to be supplied into the ink reservoir, it is sufficient to handle the ink pellets themselves, and there is no necessity to utilize separate structures as closure members.
Advantageously, the inlet port is defined by a flexible membrane which can be reversibly deformed when an ink pellet is pressed there through. Depending on the size and configuration of the ink reservoir, the ink pellet held in fitting engagement in the inlet port will be subject to the heat of the melted ink in the ink reservoir to a greater or lesser extent. In a preferred embodiment the inlet port should therefore be thermally insulated from or shielded against the melted ink and/or the heating system of the ink reservoir at least to such an extent that the ink pellet serving as the plug for closing the inlet port will not be melted and become dislodged before it is pressed into the ink reservoir and replaced by a new pellet. To this end, a heat shield may be provided inside of the ink reservoir, and/or a sufficient distance may be provided between the inlet port and the space accommodating the melted ink. If the walls of the ink reservoir are made of a material having a high heat conductivity for heating the ink or achieving an even temperature distribution, then the wall portions of the heat reservoir defining the inlet port may be made from a different material having a smaller heat conductivity.